Sauté onions, mushrooms, and celery while stirring frequently for about 5 minutes or until the vegetables begin to soften.
Add the minced garlic and sauté for another minute or so.
Add the wine, fish stock (or water), the diced and grated potato, bay leaf and oregano.
Bring to a boil.
Cover, reduce heat and simmer for about 10 minutes or until potatoes are tender.
Add the fish, cover and simmer for 3-5 minutes or until the fish is opaque and flakes easily.
Add the corn and milk and heat through.
Discard bay leaf.
Season to taste with salt and pepper.
Just before serving add lemon juice and garnish with parsley